Flytrex Core v2 Altitude looks wrong

[stevejluke]

Hi all,

I added a Flytrex Core v2 to my Phantom 2 the other day, but it looks like the altitude is mis-behaving. For example, this last video I launched from the top of a hill, flew around some, then landed at the bottom of the hill. The altitude at times shows I went below my landing point when I was hovering above my head at the top of the hill. In Dashware, I set up Height to be the distance above the landing point, since it was the lowest position in the flight (in reality). But at one point in the video (around 7.5 minute mark) I touch down about 3 feet from the final landing point and it says I am +20 feet in altitude. Some time later (about 8.5 minute mark), I do another touchdown and it says I am -40 feet.

I have my flytrex module mounted on the top-front of the quad, midway between the rotors.



There is plenty of air back there I think, and no direct sunlight.
Here is a link to the mission: Here
Here is a link to the video: [youtube]https://www.youtube.com/watch?v=BmnjmqU6Mjo[/youtube]. I had an earlier crash which made the gimbal wonky, so please forgive the jitters in the camera (the crash didn't affect the Flytrex, I hadn't put it on yet).

I would appreciate any suggestions on getting altitude to work. Thanks.

 

[rrmccabe]

I think its pretty common. Mine did it when it was first new at -25' in same spot I took off but it seems to have improved. I haven't been paying as much attention to it but will try to watch it.

Give it a few flights and see if it gets better.

 

[Ohary]

Not sure how flytrex computes elevation. If it's by GPS, I can tell you from experience using GPS for survey grade elevations, the vertical error is usually about 2x the horizontal error. Without post processing error correction, GPS is only accurate to about 15'horizontal and therefore about 30' vertical.

If it's using some form of a barometer, it will likely be more accurate, but pressure could be affected by the props. But also remember barometric pressure is only as accurate as the weather, i.e. there will be elevation errors based on how stormy or nice it is.

 

[rrmccabe]

Not sure how flytrex computes elevation. If it's by GPS, I can tell you from experience using GPS for survey grade elevations, the vertical error is usually about 2x the horizontal error. Without post processing error correction, GPS is only accurate to about 15'horizontal and therefore about 30' vertical.

If it's using some form of a barometer, it will likely be more accurate, but pressure could be affected by the props. But also remember barometric pressure is only as accurate as the weather, i.e. there will be elevation errors based on how stormy or nice it is.

They have an on board barometer. I would not think the weather would effect it to much on a regular basis as it just zeros when you power up and give a reference elevation on that.

The weather should not change drastically enough in 5-10 minutes to make 40' swings in elevation.

 

[Ohary]

I wonder how much error can/could be caused by pressure differences from prop wash?

Off topic, but are you familiar with the flytrex live? Does it need a cell phone connection?

 

[rrmccabe]

I wonder how much error can/could be caused by pressure differences from prop wash?

I don't know. As I mentioned above mine seemed to settle down and working good.

Off topic, but are you familiar with the flytrex live? Does it need a cell phone connection?

Yes, I am. I ordered a Live and cancelled order. They require a SIM card and cell connection. Depending where you are they might not work. In my location (US) they rely on old 2G technology from T-Mobile which is currently unreliable and on its way out.

 

[stevejluke]

I wonder how much error can/could be caused by pressure differences from prop wash?

I think this is a probable cause. I thought putting it on top would keep the space on the bottom from getting too filled up, with the gimbal, gimbal noise reduction circuit, and vTX, it is pretty crowded down there. I will put it on the bottom tonight and let you know.

 

[stevejluke]

Yeah, it appears to have been caused by prop wash. I moved it under the phantom's body and the altitude seems to be right-on. Thanks for pointing me in the right direction.

 

[chapsrlz]

Yeah, it appears to have been caused by prop wash. I moved it under the phantom's body and the altitude seems to be right-on. Thanks for pointing me in the right direction.

could you post a pic?

i placed mine on one of the legs (as recommended by arthur konze) and im pretty sure the core is reading a lower value. in a couple missions i've sent the quad up until i almost cant see it, and my record is 488 feet :/

http://www.flytrex.com/mission/quadcopt ... cer-67176/

 

[stevejluke]

Don't have pics of position now, but mine is almost same spot, but on the inside of the leg, so the aircraft's body is directly above it.

I haven't done an absolute height test with it, I live close to a small airport so don't go much above roof tops so I don't get in the way of flight approaches. But in tooling around the yard, top of hill to bottom of hill, top of house, etc, it seems to match the telemetry fed back from the iOSD mini pretty closely and is pretty close to what I would expect now.

 

[rrmccabe]

Here is mine. I just drilled two small holes into the battery compartment and used a zip tie. There is over a mm of distance between the barometric pressure sensor and the body and kept it out of the sun as recommended.

 

[chapsrlz]

this is where i had my flytrex

moved here:





and boooooooooom new record
391 mts max ascent (1283 ft)
http://www.flytrex.com/mission/quadcopt ... cer-69723/

 

[rrmccabe]

Thats probably one of the better mounting locations I have seen. I would think that work work OK as long as you are not getting any air from the props.